1. Field of the Invention
The invention pertains to a device for an automobile or any other type of motor vehicle powered by an internal combustion engine for continuously providing a measure of the economy of operation of the vehicle. More particularly, the invention relates to a device which provides the operator of a motor vehicle with a continuous indication of the rate of fuel consumption readable directly in miles per gallon, kilometers per liter or any other desired measure of the rate of fuel consumption. The device may also provide other tests or checks of operating economy.
2. Description of the Prior Art
It was recognized early in the history of the development of internal combustion engines that the vacuum, or more precisely the relative pressure below atmospheric pressure, in the intake manifold of an internal combustion engine is related to the rate of fuel consumption and hence to the operating economy of the vehicle powered by the engine. Numerous devices have been developed during the preceding decades which in some way have taken advantage of this fact. The great majority of these devices gave a simple "yes" or "no" type indication of whether or not the vehicle was then being operated in an economical manner. For example, a lamp would be lit or a meter dial would deflect past a marker point when the vacuum in the intake manifold fell below a predetermined level. Unfortunately, these devices provided only an extremely rough indication of operating conditions to the operator of the vehicle employing the instrument. The indication given was subjective, being dependent upon an arbitrary pressure as a cross-over point between economical and uneconomical operating conditions. The operator was given no numeric or accurate indication of precisely the current rate of fuel consumption. Nor could the operator determine from such devices whether an indication of uneconomical operation was indicative of poor driving habits or of a mechanical problem with the engine.
At a comparatively late date devices were developed which directly measured fuel consumption by measuring the rate of flow in the fuel line between the fuel tank and carburetor. Flow rate measuring devices have been found to be inherently more expensive than pressure measuring devices. Often, electronic circuitry is required to translate the output of a fuel flow measuring device into a usable indication. Of course, the price of the total apparatus in that case is unduly expensive and often prohibitive.
Furthermore, none of the devices of the prior art were capable of providing an operator of a motor vehicle with an indication of whether or not the vehicle was then operating and being operated to achieve the maximum possible fuel economy, that indication being made for the normal range of operating speeds of the vehicle. Nor did the devices of the prior art indicate at engine idle speed and conditions whether the engine was in proper tune and operating at maximum efficiency and economy.